Feature Request: ARM64 Support

Hello! With the recent switchover of Macs to ARM (M1/M1Pro/M1Max) I've been unable to use the postgresql-hll module without emulating x86 in Docker. Would it be possible to get a version built for ARM?

I believe it could be as simple as adding the following to your Travis file:

```
arch:
- amd64
- arm64
```

https://docs.travis-ci.com/user/multi-cpu-architectures/

Happy to help out as well if you like.

Thanks,
Justin